1. Field of the Invention
The present invention relates to a lens device, an imaging apparatus having the same, and a method of detecting a position of a movable lens mounted on the lens device.
2. Description of the Related Art
In recent years, there has been progress in an increase in resolution and an increase in size of screen such as a television or a monitor, and there has been an increase in the demand for an increase in image quality of a video to be displayed. In order to cope with the demand for an increase in image quality, a lens device for movies, broadcasting, and the like has been equipped with a position detection device capable of detecting the position of a movable lens such as a zoom lens with a high accuracy. In such a manner, an increase in performance of lens control is achieved.
As the position detection device, there is a device that directly detects movement of the movable lens in the optical axis direction and detects the position of the movable lens (refer to JP1989-97911A (JP-H01-97911A)). Further, there is a device that detects movement of a rotating member rotating about the optical axis in conjunction with movement of the movable lens and detects a position of the movable lens (refer to WO2013/114705A).
The lens device described in WO2013/114705A is provided with two magnetic recording members for a rotating barrel that rotates in accordance with movement of the zoom lens. The lens device detects an A phase signal, which corresponds to a magnetic signal having a first wavelength recorded in one magnetic recording member, and a B phase signal, of which the phase deviates from that of the A phase signal, and detects a C phase signal, which corresponds to a magnetic signal having a second wavelength recorded in the other magnetic recording member and different from the first wavelength, and a D phase signal of which the phase deviates from that of the C phase signal. Thereby, the lens device calculates a phase difference between the A phase and the C phase by using the A B CD phase signals, and detects the position of the zoom lens based on the phase difference.
Further, a device that detects the position of a movable lens through the combined use of a potentiometer, which directly detects movement of the movable lens in the optical axis direction, and a photointerrupter which detects movement of a rotation plate rotating in conjunction with the movement of the movable lens has been also proposed (refer to JP1995-230031A (JP-H07-230031A)).
In the device described in JP1995-230031A (JP-H07-230031A), the accuracy in position detection is improved by correcting the position of the movable lens, which is detected by the potentiometer, based on the signal detected by the photointerrupter.